Many heart patients have partial heart function and could benefit from a chronic or long-term ventricular assist device. There is no such chronic assist device in use at this time. Artificial hearts, either complete or partial, have been implanted as a temporary bridge to a heart transplant. These devices replace rather than assist normal heart function. Two main categories of assist devices are being developed and analyzed. One utilizes portions of an artificial heart or a comparable apparatus connected between the heart and aorta. These devices, although they are implanted and use an internal power source, are intended as a short term bridge to a transplant. The other category is counter pulsation devices which attach to the aorta. Blood flows passively to a collapsible chamber during systole. The chamber is then collapsed and the blood forcibly returned to the aorta.
Acute or short term ventricular assist devices presently used are of two principal types. Neither is used for chronic use. One has a counter pulsation action and is exemplified by use of an intra-aortic balloon. The balloon is collapsed during systole, providing an empty space to be filled with blood pumped by the heart. As the space is empty, the heart operates against little resistance. The balloon is then expanded, forcing blood through the arterial system. This type of ventricular assist is unsuitable for chronic use as it requires a pneumatic connection through the subject's skin for contraction and expansion of the balloon. Infection is likely to occur. The second type of acute assist device utilizes an extracorporeal pump, as the Biomedicus centrifugal pump. Again, connection through the skin is required for the pump inlet and outlet with a risk of infection. In both such systems, vigorous anticoagulation therapy, which is not feasible for long term use, is required.